The overall objective of the research program has been to study the non-steady burning characteristics of solid rocket propellants, both experimentally and theoretically, to establish a basis for avoiding combustion instability in rocket motors and for predicting thrust transients during motor ignition and extinction. A new non-steady burning model for composite propellants was formulated in which the key element, the non-steady heat feedback law from the gaseous flame, was shown to be a function of the instantaneous pressure and burning rate. Solutions to this model showed that burning stability is largely determined by the exothermicity of reactions in the immediate neighborhood of the propellant surface and by the sensitivity of burning rate to surface temperature. The predictions of the model were generally confirmed by T-motor and rapid pressurization experiments. The non-steady burning model was also used to analyze L-star combustion instability in rocket motors and to demonstrate the feasibility of a novel mechanism for suppression of combustion instability by aluminum addition to a propellant. (Author).

Despite significant developments and widespread theoretical and practical interest in the area of Solid-Propellant Nonsteady Combustion for the last fifty years, a comprehensive and authoritative text on the subject has not been available. Theory of Solid-Propellant Nonsteady Combustion fills this gap by summarizing theoretical approaches to the problem within the framework of the Zeldovich-Novozhilov (ZN-) theory. This book contains equations governing unsteady combustion and applies them systematically to a wide range of problems of practical interest. Theory conclusions are validated, as much as possible, against available experimental data. Theory of Solid-Propellant Nonsteady Combustion provides an accurate up-to-date account and perspectives on the subject and is also accompanied by a website hosting solutions to problems in the book.

A prominent mode of coupling that may drive a solid propellant rocket motor into instability is the interaction between the oscillatory gas dynamic pressure at the burning surface and the instantaneous rate of the oscillatory pressure fluctuations and of rapid monotonic pressure increases are being investigated in a continuing program. Two pieces of apparatus are in use for this purpose. One is the T-tube oscillator. The latter is a chamber with a device to change suddenly on command the throat area of the nozzle to produce pressure rise times of 8,000 psi per second and less. This low range supplements the higher range achievable in the T-tube oscillator. The chamber has three quartz windows which allow luminosity measurements and high speed motion pictures of the propellant flame to be made along with chamber pressure. By varying the chamber volume, and thereby the dp/dt, luminosity versus pressure can be obtained as a function of dp/dt. From this, the temperature is plotted as a function of pressure and dp/dt, and therefore the entropy is plotted as a function of the same variables. The brightness-emissivity method of instantaneous flame temperature measurement is being used. Experiments are being conducted to determine the flame temperature as a function of pressure in various regimes of dp/dt. (Author).

A fundamental study of the non-steady combustion of solid propellants with application to rocket instability is described. A film strip of a metallized solid propellant burning in an oscillating pressure field was analyzed in order to determine the phase relationship between the imposed pressure maxima and an apparent wave of luminosity in the combustion gases. The implications of these observations as they affect the model of the burning propellant are briefly considered. Two types of experimental observation which will be used to study non-steady combustion are outlined. One method involves the measurement of the temperature of the combustion gases downstream from the flame zone. The use of a particle track method for the observation of pressure-velocity relationships in the burnt gases is also considered. (Author).

Pressure and velocity coupling effects on combustion stability in solid propellant burning.

A multi-dimensional numerical model has been developed for the unsteady state oscillatory combustion of solid propellants subject to acoustic pressure disturbances. Including the gas phase unsteady effects, the assumption of uniform pressure across the flame zone, which has been conventionally used, is relaxed so that a higher frequency response in the long flame of a double-base propellant can be calculated. The formulation is based on a premixed, laminar flame with a one-step overall chemical reaction and the Arrhenius law of decomposition with no condensed phase reaction. In a given geometry, the Galerkin finite element solution shows the strong resonance and damping effect at the lower frequencies, similar to the result of Denison and Baum. Extended studies deal with the higher frequency region where the pressure varies in the flame thickness. The nonlinear system behavior is investigated by carrying out the second order expansion in wave amplitude when the acoustic pressure oscillations are finite in amplitude. Offset in the burning rate shows a negative sign in the whole frequency region considered, and it verifies the experimental results of Price. Finally, the velocity coupling in the two-dimensional model is discussed. Chung, T. J. and Park, O. Y. Unspecified Center NAG8-627...